1. Field of the Invention
The present invention relates to inspection devices such as electron microscopes which are used to generate images of specimens (e.g., silicon wafers, etc.) using electron beams. More particularly, the present invention relates to systems and methods used to affect imaging time and image brightness and contrast characteristics within such inspection devices.
2. Description of the Related Art
Electron beam type inspection devices such as scanning electron microscopes are well known. Typically, such devices generate images of specimens (e.g., silicon wafers, etc.) by causing a focused electron beam projected in the form of a spot to scan a specimen surface to allow detection of reflected and other second order electrons. For example, such scanning electron beam type inspection devices are used during integrated circuit and corresponding silicon wafer production and processing.
Despite their widespread use, conventional scanning electron beam type inspection devices such as electron microscopes are not without their problems. For example, because conventional scanning electron microscopes scan specimens with an electron beam projected in the form of a spot having a relatively narrow diameter, substantial time was required to detect reflected and other second order electrons and to generate corresponding sample images. And, unfortunately, when detection times were shortened by improvements in devices to increase beam scanning speeds, the quantity of electrons emitted/detected per picture was reduced. Such reduction in the quantity of emitted/detected electrons brought about the corresponding problem of a reduction in image brightness and contrast.
To address the aforementioned problems, various devices and methods have been proposed. For example, detection devices which aim to reduce detection times such as during specimen defect detection were proposed in Japanese Laid-Open Patent Nos. 7-181297 (U.S. Pat. No. 5,498,874) and 7-249393 (U.S. Pat. No. 5,576,833). With such detection devices, an electron beam emitted from a rectangular cathode is irradiated on the surface of a specimen after being formed by plural multi-polar lenses into a rectangular or elliptical cross sectional shape. As shown in a drawing figure identified as xe2x80x9cFIG. 1xe2x80x9d which is attached to this patent document, a beam spot of rectangular shape allows for relatively shorter scan times relative to a particular specimen (e.g., a silicon wafer, etc.) as compared to conventional spot-form electron beam type devices since more surface area was covered with each successive scan. Unfortunately, although such improved detection devices have significantly reduced detection times because beam spots have increased in extent (size and shape), they have not fully addressed other problems associated with scanning specimens such as controlling detected image brightness and contrast.
Thus, there exists a need to solve the aforementioned problems associated with prior electron beam type inspection devices and to provide new and improved electron beam type imaging devices such as new and improved scanning electron microscopes. To be viable, such new and improved electron beam imaging devices must allow for fast scanning times and the generation of images having constant brightness and contrast characteristics.
In view of the aforementioned comments concerning the problems associated with prior electron beam type inspection devices, the present invention provides an inspection device which allows for faster picture detection and which is capable of producing images having normal and constant brightness and contrast characteristics regardless of observation magnification, etc. As such, users of electron beam type inspection devices can now take advantage of the present invention to produce images (e.g., such as silicon wafer surface defect images, etc.) without having to realize poor image qualities that often resulted from use of prior devices.
The present invention solves the aforementioned problems and provides the above-stated benefits by providing new and improved electron beam type inspection devices that allow for fast scan times and which are capable of producing images of samples that have normal and constant brightness and contrast characteristics. For example, according one aspect of the present invention, provided is an inspection device that includes an electron gun which emits an electron beam, an electron beam optical system which causes the electron beam to form an irradiation region on a surface of a specimen, a detector which detects at least one of second order electrons and reflected electrons reflected by the irradiation region, and a projection optical system projecting the second order electrons and the reflected electrons onto a detection surface within the detector. The second order electrons and the reflected electrons correspond to an observation region within the irradiation region. The inspection device also includes a magnification controller which controls the size of the observation region and the magnification of the projection optical system, and an irradiation controller which controls the current density or intensity of the irradiation region based on the size of the observation region.
According to another aspect of the present invention, provided is an inspection device that includes an electron gun which emits an electron beam, an irradiation electron optical system which irradiates the electron beam to an irradiation region on a surface of a specimen, an electron detector which detects at least one of second order electrons and reflected electrons which are generated by the irradiation region, and a projection optical system which projects to a detection surface within the electron detector an observation region within the irradiation region on the specimen to cause imaging of the observation region. The observation region corresponds to a second order beam which includes at least one of the second order electrons and the reflected electrons. The projection optical system is disposed between the specimen and the electron detector. The inspection device also includes a magnification controller coupled to the projection electron system and which changes the size and area of the observation region on the specimen surface and which changes the projection magnification of the projection optical system. The inspection device also includes an electron irradiation controller coupled to the irradiation electron optical system and which changes the current density and intensity of the irradiation region according to the size and area of the observation region. The electron detector adjusts electron detection sensitivity based on the projection magnification set by the magnification controller.
And, according to another aspect of the present invention, provided are methods of making inspection devices as described above. Such methods include steps of providing and assembling the aforementioned component parts to make corresponding inspection devices.